Systems of this type include an air blower which is arranged to take air from outside the vehicle or air recycled within the vehicle, and to deliver air to a distribution casing which includes air reheating means and distribution vents, so as to distribute the air delivered under pressure, and optionally heated, into the cabin of the vehicle. The blower includes a chamber in the form of a volute, in which a blower rotor, driven by an electric motor, is mounted. The volute has an air inlet for admitting air from outside the vehicle or recycled air, together with an air outlet for the air delivered under pressure by the blower. This air outlet is connected to the distribution casing through an appropriate duct which may have an evaporator mounted within it if the installation is also an air conditioning system. One installation of this type is known, in particular, from the specification of Japanese patent application No. 54-138238.
Mass produced vehicles are arranged to be provided with either right hand drive, that is to say with the driver sitting on the right of the vehicle, or with left hand drive, that is to say with the driver sitting on the left hand side, as required. For reasons connected with the layout under the hood of the vehicle, it is generally necessary to provide that the blower is arranged on the opposite side of the vehicle from the driver, that is to say on the right hand side if the vehicle is of left hand drive, and vice versa. This has hitherto made it necessary to provide blower units which are specifically adapted according to whether the vehicle is of the left hand drive or right hand drive type. In practice this means that two types of blower unit must currently be provided, these being substantially identical except that they are "mirror images" of each other.